Patent GB-957087-A (GB)
Title: The manufacture of electrode structures and the structures thus formed
IPC: H01J29/82
Filed: 1961-10-31
Abstract: 957,087. Cathode-ray tubes. TEKTRONIX Inc. Oct. 31, 1961 [June 12, 1961], No. 38940/61. Heading H1D. [Also in Division B3] In a method of making an electrode structure, e.g. the electron gun assembly of a cathode-ray tube, a body is formed having surfaces of the desired electrode configuration and on which the electrodes are formed as coatings; afterwards the body is destroyed or withdrawn without deforming the electrode coating structure. In the complete process the body shown in Fig. 3 is formed in the mould of Fig. 8 (made of two pieces so as to be readily removable) by an injection moulding technique and is covered with masking material 64, Fig. 3, on those parts which represent spaces in the final electron gun structure, Fig. 1. The masking material, e.g. paraffin or vinyl plastic, may be applied indirectly by placing it in the mould before the moulding process or by painting or by applying pressure-sensitive tape. Support pins 38, 44, 46, Fig. 1, and insulator, e.g. glass or ceramic, support rails 34 are then assembled, e.g. by moulding glass rods around the pins or by pressing two glass bars, which together form each insulating rail 34, together around the interposed pins. The ends of the pins remote from the electrodes are then masked and the pin-insulating rail assemblies held in a jig, while the pins are fused to the body of Fig. 3, or the support pins may be attached to the body during the moulding operation, or the insulating support rails may be positioned in the mould and the body cast with parts surrounding the rails in place of the pins. The complete body is then coated with conductive material, e.g. by electroplating, vapour deposition, metal spraying or by an electrodeless plating technique in which a metal compound in solution is decomposed by contact with the body without the use of an electric current. A suitable material for the body is Wood's metal which is removed from the coating structure by melting and draining. Residual Wood's metal is removed by chemical etching and the coating structure is then polished. A suitable material for electroplating is silver or copper, or alternate coatings of silver, copper and silver may be built up. The electroplating process is preceded by a striking step to produce a fine-grained base of crystals upon which the plating material is deposited as a uniform coating. The mounting of the completed support rails on the destructible body may take place after the body has been coated. Instead of using insulating support rails, metal support rods or a single supporting metal frame with a plurality of pin projections which may be separated later may be used. The pins may be sealed in slits in the glass envelope of a cathode-ray tube by means of glass frit. Using Wood's metal and silver electroplated coatings the ends of the pins are silver plated and coated with indium. Instead of using Wood's metal (50% Bi, 25% Pb, 12.5% Sn and 12.5% Cd) other low-melting point alloys may be used, e.g. 44.7% Bi, 22.6% Pb, 8.3% Sn, 5.2% Cd and 19.1% In or 58% Bi and 42% Sn. The material of the body may be etched out instead of melted out. Wax or a plastic, rendered conductive by filling with graphite or metal powders or by metallizing the surface may be used instead of metal. If a permanent body is used which is withdrawable from the structure a suitable material is iron, nickel, brass or stainless steel. The cathode and control grid of the electron gun are preferably formed separately from the electrode coating structure, but the control grid may form part of this structure. In the electron gun structure of Fig. 1, electrodes 18 and 20 are shields.